1. Field of the Invention
The present invention relates to welded steel pipe steel and welded steel pipe having good inner surface wear resistance as required in such fields as oil and natural gas drilling and transportation, and to a method of manufacturing same.
2. Description of the Prior Art
In recent years the requirements for the wear resistance properties of the inner surface of steel pipe have been increasing. In drilling for oil and natural gas a considerable amount of the related exploitation work involves horizontal drilling operations. A problem that arises during such operations is that of damage to the inner surface of casing pipe from wear caused by contact between the drill pipe and the casing pipe. There is also a demand for slurry pipe having an inner surface that is more wear resistant.
Wear resistance can be effectively improved by increasing the hardness of the steel, as is disclosed by JP-A-62-270725. However, from the viewpoint of achieving both corrosion resistance and low-temperature toughness, hardening the whole of the steel pipe is undesirable. In recent years, thermal spraying of dissimilar metals and ceramics and the like, surface treatment processes and other such techniques for hardening just the surface region of steel pipe have been investigated but in each case have been found to lack sufficient productive efficiency.